This invention relates in general to vehicle brakes and, in particular, to an improved rotor for use in a disc brake assembly, and method for finish machining the friction disc faces of the rotor.
A conventional hydraulic disc brake assembly includes a brake caliper and a rotor. The brake caliper is secured to an unsprung suspension component of the vehicle, and includes a pair of brake friction pads and a hydraulically actuated piston. The rotor is rotatably supported relative to the caliper, and includes a mounting flange and an outer annular friction disc. The friction disc defines generally parallel machined inner and outer faces adapted to be frictionally engaged by the friction pads. When the disc brake assembly is installed on a vehicle, the friction disc is disposed between the friction pads. When the piston is hydraulically actuated, the friction pads are urged into frictional engagement with the friction disc to brake the vehicle.
During the manufacture of the rotor, the inner and outer faces of the friction disc are machined during a final finishing operation to predetermined tolerances. Typically, this "finish machining" of the friction disc is accomplished by simultaneously grinding the inner and outer faces against a pair of grinding wheels, or by turning the faces on a lathe against a pair of conventional cutting tools. The "simultaneous" finish machining operation reduces the overall machining time and enables tighter tolerances to be maintained.
Conventionally, a "continuous" method for finish machining the inner and outer faces of the friction disc utilizes a CNC (computer numerical control) lathe. The CNC lathe includes a pair of cutters located on opposite sides of the friction disc, and initially positioned at either the extreme inner or outer diameter of the disc. During machining, the cutters are continuously moved in either an inward or outward radial direction (depending on their initial position) relative to the axis of the rotor as the rotor is turned. While appearing to produce substantially flat surfaces, the cutters are actually operative to machine a narrow shallow spiral groove in each of the inner and outer faces of the friction disc.
It is also known to finish machine the rotor friction disc faces by using an "interrupted" turning method. According to this method, the cutters machine in a radial direction relative to the axis of the rotor to a predetermined distance, at which point the cutters dwell for a single rotation of the rotor. This creates a single groove extending circumferentially around the friction disc a full 360.degree.. The cutters continue on machining in the radial direction until the next predetermined distance is reached, at which point the cutters dwell for a single rotation of the rotor to form another, separate groove. This pattern is repeated throughout the finish machining operation to produce progressively smaller circumferential grooves.